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States that legalized marijuana have higher rates of mental illness, study says

For the past 20 years, scientific studies have warned that heavy marijuana use can lead to schizophrenic episodes and psychotic disorders.

Now, in the first study of its kind, RTI International in Research Triangle Park suggests marijuana may carry other risks as well.

The research organization said Monday that states with permissive medical marijuana laws have significantly higher rates of serious mental illness. The study, published in the peer-reviewed International Review of Psychiatry, was based on data involving 630,000 people interviewed between 2008 and 2015.

RTI’s study doesn’t explain the causes of the relationship between marijuana legalization and mental illness. It’s possible that states with higher rates of serious mental illness were quicker to legalize medical marijuana, said Lauren Dutra, a social scientist at RTI and the lead author of the study.